The avast script blocker is a) only available in the Pro version, which I presume you have, b) only works with certain browsers and firefox isn't one.
A script, is a term for a piece of code that executes a function (a small program), that can be many different things, javascript, JAVA, Visual Basic, etc. an on a supported browser (Netscape, Mozilla not firefox and IE) that avast script blocker would first intercept the script and examine it for malicious content.
By Outlook you don't confirm if this is Outlook Express or MS Outlook two entirely different email clients.
Outlook Express uses this draconian, read crazy, measure to supposedly protect the user from potential viruses, it doesn't scan just blocks because these file types could be infected, not that they are infected.
A batch file (.bat) is just a text file (that can be run), which contains a number of commands designed to carry out a task. Whilst not technically a script, it can run commands that are scripts. The .xls and .doc files of Word and Excel can have Macros to do functions within the document and macros can be malicious also.